Riser for Coil Tubing/Wire Line Injection

ABSTRACT

The present invention is directed to a system including a self supporting riser (SSR) which is connected to a well to provide fluid communication to fossil hydrocarbon reservoirs deep below the seafloor. The SSR is constructed of a plurality of joints comprising regular joints and specialty joints that define the SSR and are selected to optimize the SSR for a well in a specific location. A unique aspect of the invention is further directed to a small vessel subject to high vessel motions that permits a coil tubing/wire line system to be mounted on a stabilizer system mounted on the vessel. The riser extension that connects the vessel to the self supporting riser preferably has a telescopic joint/section that is designed for the heave of the vessel.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of Ser. No. 12/714,919 filed Mar. 1, 2010, entitled “Riser Technology”, which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF INVENTION

The present invention is directed to the interfacing of a Self Supporting Riser (SSR) to a vessel subject to high vessel motions of pitch and roll. The small vessel employs a unique stabilization system for supporting a coil tubing/wire line injector and supporting equipment on the vessel.

BACKGROUND OF THE INVENTION

It has been the practice for the intervention in deep wells that recover hydrocarbons from fossil hydrocarbon reservoirs deep below the Gulf of Mexico and other offshore areas to use very large vessels of various designs upon which the equipment for intervention into the wells are supported. These vessels cost millions of dollars and have day rates that frequently can not be cost justified to perform work-over coil tubing/wire line procedures.

SUMMARY OF THE INVENTION

The present invention is directed to a system including a self supporting riser (SSR) which is connected to a well to provide fluid communication to fossil hydrocarbon reservoirs deep below the seafloor. The SSR is constructed of a plurality of joints comprising regular joints and specialty joints that define the SSR and are selected to optimize the SSR for a well in a specific location. A unique aspect of the invention is further directed to a small vessel subject to high vessel motions that permits a coil tubing/wire line system to be mounted on a stabilizer system mounted on the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a Self Supporting Riser (SSR) connected to a well for producing hydrocarbons from a fossil hydrocarbon reservoir deep below the seafloor, and a small vessel subject to high heave, pitch and roll outfitted for downhole intervention through the SSR;

FIG. 2 is a schematic view of another embodiment of the stabilizer system for the intervention system to inject a coil tubing/wire line into the SSR;

FIG. 3 is a schematic view of the detail of the telescoping section of the riser connection from the SSR to the vessel near its midpoint;

FIG. 4 is a schematic view of the detail of the telescoping section of the riser connection from the SSR to the vessel at the upward position of heave of the vessel; and

FIG. 5 is a schematic view of the detail of the telescoping section of the riser connection from the SSR to the vessel at the downward position of heave of the vessel.

DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, reference is made to Ser. No. 12/714,919 and the drawing therein for a more detail description, a novel Riser Vessel Interface System (RVI) 60 facilitates using the SSR for downhole intervention and workover through the SSR 10 using relatively small vessels. The nature of an SSR is such that it may be relatively sensitive to the magnitude of externally applied tension and to variations in externally applied tension. It is the nature of small vessels that their motions in response to waves and swells are greater than those of larger vessels and substantially greater than the motions of platforms or floating production facilities. The interface between an SSR and a small vessel therefore requires a greater range of motion and less tension variation than is provided by the previous art. The coiled tubing injector must be supported by the vessel, and the weight of deployed tubing normally hangs from the injector.

Referring to FIG. 1, intervention vessel 35, with reel 59 and crane 46, is shown with coil tube injector 120 assembled on the RIV System 60 (not shown). The desired downhole tooling has been attached to the coiled tubing and made ready for operations. The above equipment and its specific arrangement provide a novel arc of tubing 61 to be used in the present invention to extend the fatigue life of the tubing 63. (see also FIGS. 14 and 14A of Ser. No. 12/714,919). This allows the SSR to be fixed to the earth while the reel moves with the deck of the vessel. As described in Ser. No. 12/714,919, riser extension 64 has a telescoping joint/section 65 that is present as a contingency for exceptional heave.

FIG. 2 illustrates the combination of an SSR, a riser extension 64 between a vessel 35 and, a telescoping joint/section 65, and a pitch roll stabilized frame 68 to engage the SSR to a vessel subject to high vessel motions. The method for using this combination allows the system to function without stroking heave cylinders of the RVI structure The riser extension with telescoping provisions 65 is engaged to the top of the SSR by connector 92 and hangs from the pitch and roll stabilized frame 68 which is in turn supported by heave platform 66 that in this embodiment may be attached to the deck 33 of vessel 35. The attachment point between the frame 68 and the riser extension 64 is preferably near the vessel center of motion and preferably in a moon pool of the vessel 35.

FIG. 3 illustrates the mid heave position. The telescopic function of riser extension 64 is allowed to extend and retract with telescoping section 65 as the vessel heaves. The allowable range of vessel heave with respect to the SSR is as great as the allowable travel length of the telescope. Stops can be built into the telescopic joint 65 to limit the minimum and/or maximum extension. Hydrostatic lock is prevented by venting the telescopic section so that fluid can flow into and out of it as the length and internal volume change. Venting can be through ports open to seawater or through a line 55 to a supply of water or other fluid that may be filtered or otherwise treated or constituted to reduce corrosion and avoid debris and contamination and enhance lubrication. It is apparent that the effective weight below the attachment point can be increased or decreased by using line 56 to trim the pressure of fluid in chamber 69 in a way that causes the telescopic joint/section to pull on or push against the SSR while flow into and out of line 56 allows the telescoping section to extend and retract. Chamber 69 is similar in construction to the rod end of a hydraulic cylinder. FIG. 4 illustrates a heave downward; and FIG. 5 illustrates a heave upward.

Friction in the telescopic joint can be reduced by methods such as filling the volume with lubricating fluid, securing bearings such as balls between the moving parts of the telescopic section, using a liner of material such as ultra high molecular density polyurethane, or some combination of similar methods.

Verticality of the riser extension is aided by any combination of weight below the point where it attaches to the pitch and roll stabilized frame, stiffness below the attachment point, and active control of the hydraulic cylinders that support the pitch and roll stabilized frame. The righting moment due to weight below the attachment point is proportional to the weight times the distance between the center of gravity and the attachment point; and the apparent weight can be increased by applying pressure through line 56. Stiffness of the riser extension, in combination with attachment of the lower end of the extension to the SSR, allows the stiffness of the riser and the righting moment of the buoyancy module to counteract any overturning moment introduced by the weight of equipment supported above the attachment point. The righting moment of the buoyancy module is proportional to the buoyancy force, the angle of inclination, and the distance between the center of buoyancy and the effective “hinge point” where the riser can curve below the buoyancy.

As further described in Ser. No. 12/714,919, a valve assembly can be used to prevent exchange of fluid between supporting cylinders for the pitch and roll stabilized frame, thereby locking the riser extension assembly and its load in position so that it pitches and/or rolls with the vessel. Locking the assembly may be advantageous at times when the extension is not connected to the SSR.

As described in Ser. No. 12/714,919, the pitch and roll stabilized frame supports the riser extension in a way that exerts equal lifting force symmetrically around the riser extension regardless of the pitch or roll angle of the vessel. As also described in Ser. No. 12/714,919 active control of verticality can be achieved by trimming the lifting forces that are otherwise equally distributed around the riser extension. The load on these cylinders may be substantial, but application of a comparatively small force can trim the balance of forces to compensate for an offset center of gravity or external horizontal forces on the supported assembly. The described hydraulic cylinder arrangement allows control of the relative fluid pressure in opposing hydraulic cylinders to balance external forces such as an offset center of gravity. A feedback signal proportional to inclination of the riser extension can be used to actively control the balance of forces and thereby maintain verticality of the riser extension.

It is apparent that relative motion between the earth and any tubing suspended in the SSR can be avoided by operating the injector to run or pull a length of tubing equal to the extension or retraction of the telescopic joint, and that this could be automated by using a feedback signal from sensing the relative position of the two elements of the telescopic joint.

Maximum pitch and roll angles are limited by the range of motion of the supporting hydraulic cylinders and by potential interference with the walls of the moon pool. It is further apparent that the outer member of the telescoping joint could be either the larger or the smaller of the 2 members, and that the telescopic joint could either be part of the riser extension or be part of the SSR. The telescopic joint can include provisions for locking it anywhere between maximum and minimum extension, either by ROV or by remotely operated latches.

Equipment mounted atop the riser extension remains at a fixed elevation with respect to the vessel center of motion while pitch and roll cause the vessel to incline with respect to this equipment. The center of gravity is kept as low as is practical while providing clearance between the vessel and the outer perimeter of the equipment attached to the riser extension. This clearance and the dimensions of the moon pool determine the maximum vessel pitch and roll that can be accommodated without clashing or other interference. An advantage of this embodiment is that it keeps the center of gravity of the supported equipment low to reduce the overturning moment due to forces acting on this equipment.

It is further apparent that a hydraulic connector between the SSR and the riser extension is not necessary if one moving part of the telescopic joint is attached to the SSR and the other to the riser extension, and there is no lower stop. The vessel can then be engaged to the SSR by making up the two halves of the telescopic joint. In this embodiment the telescopic joint is free to separate and thereby release the vessel from the SSR if the vessel is forced far enough off station to cause the top of the SSR to set down by more than the maximum stroke of the telescopic joint. 

1. A stabilizer system for a vessel subject to high vessel motions of heave, pitch and roll comprising: a heave platform adapted for attachment to said vessel, a pitch and roll frame; two or more pitch and roll compensation cylinders attached to said frame, each said cylinder having a compliant coupling on each end of said cylinder, one coupling attached to said frame and the coupling at the other end of said cylinder attached to said platform.
 2. A stabilizer system according to claim 1 wherein each pitch and roll compensation cylinder is attached to said frame.
 3. A hydraulic circuit for said pitch and roll compensation cylinders of a stabilizer system according to claim 2 comprising: a pump in said circuit for adding a fixed volume of fluid to the trapped fixed volume of fluid shared by the load bearing chambers of said cylinders; and means to maintain said fixed volume of fluid between said load bearing chambers of said cylinders, wherein when increased pressure occurs in one or more of said cylinder chambers, fluid flows to the other cylinder chambers.
 4. A small sea vessel subject to high vessel motions of heave, pitch and roll and having a moon pool comprising: a stabilizer system attached to said vessel comprising: a platform attached to said vessel placing said platform over said moon pool; a pitch and roll stabilized frame; two or more pitch and roll compensation cylinders attached to said frame, each cylinder having a compliant coupling on each end of said cylinder, one coupling attached to said frame and the coupling at the other end of cylinder attached to said platform.
 5. A small sea vessel according to claim 4 wherein the load bearing chambers of said pitch and roll compensation cylinders are attached to said frame.
 6. A small sea vessel according to claim 4 wherein said pitch and roll frame is stabilized in said moon pool.
 7. A small sea vessel subject to high vessel motions of heave, pitch and roll and having a moon pool comprising: a riser vessel interface system including a stabilizer system attached to said vessel over said moon pool; and a riser extension connected to said stabilizer system, said riser extension adapted to be connected to a self supporting riser.
 8. A small sea vessel subject to high vessel motions of heave, pitch and roll and having a porch extending beyond the deck comprising: a stabilizer system attached to said vessel including: a pitch and roll stabilized frame; and two or more pitch and roll compensation cylinders attached to said frame, each cylinder having a compliant coupling on each end of said cylinder, one coupling attached to said frame and the coupling at the other end of cylinder attached to said platform.
 9. A small sea vessel according to claim 4 further comprising: an injector set on said pitch and roll frame.
 10. A small sea vessel according to claim 9 wherein said injector is a coil tubing injector.
 11. A small sea vessel according to claim 10 further including a coil tubing reel positioned near said work surface.
 12. A small sea vessel according to claim 11 further comprising: a riser extension secured to said pitch and roll frame, said riser extension aligned with said injector whereby the coil tubing injected by said injector passes through said riser extension.
 13. A small sea vessel subject to high vessel motions of heave, pitch and roll and having a work surface over exposed water comprising: a stabilizer system attached to said vessel over said exposed water including a pitch and roll frame; and a riser extension connected to said stabilizer system, said riser extension connected to a self supporting riser.
 14. A small sea vessel according to claim 13 further comprising: a framework set on said pitch and roll frame holding an injector.
 15. A small sea vessel according to claim 14 wherein said injector is a coil tubing injector.
 16. A small sea vessel according to claim 15 further including a coil tubing reel positioned near said moon pool.
 17. A small sea vessel according to claim 16 further including a straightener near said reel for changing the radius of coil tubing on said reel to an arc for entry to said coil tubing injector.
 18. A small sea vessel according to claim 17 further including a straightener near the top of said coil tubing injector for changing the radius of coil tubing in said arc for entry of said coil tubing into the riser extension.
 19. An intervention method for running coil tubing into a well on the seafloor wherein a Self Supporting Riser (SSR) is attached to the well's seafloor infrastructure and a vessel according to claim 18 which comprises operating said coil tubing injector for running coil tubing into said well.
 20. An intervention method comprising: running a coil tubing into a well on the seafloor through a self supporting riser attached on the wellhead by a coil tubing injector mounted on a small sea vessel subject to high vessel motions of heave, pitch and roll.
 21. An intervention method according to claim 20 wherein said coil tubing is drawn off a reel by said coil tubing injector forming an arc between said reel and said coil tubing injector.
 22. An intervention method according to claim 20 wherein said coil tubing is straightened as said tubing is drawn off said reel to form said arc and is straightened by said injector to pass though said self supporting riser.
 23. An intervention method according to claim 20 wherein the heave of the vessel is through a telescopic joint/section in the riser extension connecting the vessel to the self supporting riser.
 24. A small sea vessel subject to high vessel motions of heave, pitch and roll and having a moon pool comprising: a stabilizer system attached to said vessel over said moon pool including; a platform attached to said vessel; a pitch and roll stabilized frame; and two or more pitch and roll compensation cylinders attached to said frame, each cylinder having a compliant coupling on each end of said cylinder, one coupling attached to said frame and the coupling at the other end of cylinder attached to said platform; and a riser extension connected to said stabilizer system, said riser extension including a telescopic joint and adapted to be connected to a self supporting riser.
 25. A small sea vessel subject to high vessel motions of heave, pitch and roll and having a moon pool according to claim 24 further including: a coil tubing injector mounted on said pitch and roll stabilized frame.
 26. A small sea vessel according to claim 24 wherein said telescopic joint has a chamber in which said riser extension is allowed to extend and retract as the vessel heaves.
 27. A small sea vessel according to claim 26 further including a line to said chamber wherein the pressure in said chamber may be increased or decreased to pull on or push against said self supporting riser. 